Early white spruce regeneration treatments increase birch and reduce aspen after 28 years: Toward an integrated management of boreal post-fire salvaged stands

Post-harvest regeneration failure of white spruce (Picea glauca Moench [Voss]), has led to concerns of “de-coniferization” on productive site in the Alaskan boreal forest. Forest management in the region sought historically to increase spruce composition after harvest through silvicultural practices such as site preparation and assisted regeneration; however, successful reforestation requires the effects of these practices to persist over time and control non-target tree species. In order to identify the enduring effects of silvicultural regeneration practices, we sampled a large (26.7 ha) white spruce regeneration trial established immediately following a stand-replacing wildfire and subsequent salvage harvest in a productive upland forest. The original regeneration treatments followed a split-split plot experimental design on two landform types (LF), four ground scarification treatments (GST) plus a non-scarified control, and five artificial white spruce regeneration treatments (WSRT) plus a natural seedfall control (Densmore et al., 1999). Here we analyze the total biomass, stand density, and basal area for all tree species within each of the regeneration treatments 28 years post-establishment, and calculate seed dispersal distances. Our results show that compared to natural seedfall control plots, white spruce basal area was six times greater in planted seedling plots, and white spruce stem density (dbh ≥ 1.0 cm) was nearly three times greater in broadcast seeding plots. White spruce stem density from natural seedfall averaged 944 stems ha−1, but was dependent on both topographic position and distance to wind-dispersed seed sources. Our results also indicate that GST had few significant effects on white spruce basal area or stem density. However, scarification nearly doubled Alaska birch (Betula neoalaskana Sarg.) stem density and basal area compared to non-scarified control plots. Planted white spruce plots supported 19% less birch basal area, except in the most intensive scarification treatments in which birch basal area did not differ. Intensive scarification reduced quaking aspen (Populus tremuloides Michx.) basal area by half on slope plots. Our results demonstrate that early regeneration practices profoundly influence stand development beyond the stem initiation stage, but pre-fire stand type, post-fire configuration of unburned seed sources, and topographical variation play a mediating role in determining species assemblages and competitive relationships. A fire-killed stand must be considered within its ecological and landscape context to determine the probable success of a management action such as salvage and tree regeneration